1. Field of the Invention
The present invention relates to an ink jet recording cartridge in which an ink tank for holding an ink and a recording element substrate for discharging the ink are integrated, and to a method for producing the same.
2. Related Background Art
Recently, ink jet recording devices have been able to make finer ink droplets to meet higher-quality images, and is also required to print at a higher speed. As a result, the number of ink-discharging nozzles has been greatly increasing to meet these requirements. Increasing the nozzle number needs larger recording element substrates. Therefore, a recording element substrate, which includes passages for a recording solution, e.g., ink, to be directed towards nozzles, has an increased volume for hollow portions. At the same time, the ink composition is advancing year by year for improving color-developing capacity, light resistance or the like. Along with these developments, resin materials for ink jet recording devices are also required to have improved properties. Some of the resins now being developed include those for precision molding to precisely mount recording element substrates in ink jet recording cartridges in which an ink tank for holding an ink and recording element substrate for discharging the ink are integrated, those containing a smaller quantity of solute to prevent aging of ink, and those of higher barrier capacity, e.g., those including glass fibers, to prevent evaporation of ink.
The process of producing ink jet recording cartridges employs bonding such as adhesion, thermal calking and the like. Of these, a most commonly used method is ultrasonic welding, in which resin parts closely contacted by a jig are ultrasonically vibrated by a horn of aluminum or titanium to generate frictional heat, by which they are molten in the interface and fast bonded to each other, and then cooled, on account of its various advantages, e.g., capacity of bonding in a short time, and high precision, reproducibility, tightness and strength of the weld. For production of an ink jet recording cartridge having features shown in FIG. 1, the lid 7 pressed to the fixed ink tank 4 is subjected to vibration in the pressing direction (vertical vibration) to bond them to each other, because a production system can oscillate the lid 7 more easily in the pressing direction than in any other direction. In this case, the recording element substrate 2 is vibrated along (in parallel to) the ink discharging direction.
FIG. 13 outlines the ink discharging structure of the recording element substrate 2, provided on the bottom surface of the ink jet recording cartridge 1 having the ink tank 4, where 51: ink supply port, 52: heating element which generates energy needed for discharging an ink, 53: ink passage, 54: ink-discharging port, and 55: ink-discharging port plane. As shown, an ink is discharged in the direction, designed at a right angle to the plane 55 of the ink-discharging port.
However, ultrasonic welding causes problems, when used for the ink tank made of a noryl-based resin compounded with around 25% of glass filler for improved barrier capacity, described above. In the production step for bonding the lid to the ink tank to which the recording element substrate has been attached, high-frequency (20 kHz) vertical vibration, applied by the conventional method to the lid 7 in the pressing direction, is transmitted to the director 9 and, in turn, to the outer peripheries of the ink tank 4 of a filler-containing material, with the result that the bottom surface of the ink tank 4 oscillates at a high frequency. The vibration is further transmitted to the recording element substrate 2 attached to the bottom surface of the ink tank 4, to oscillate, at a high frequency, the ink discharging structures, e.g., a number of the ink passages 53 having hollows in the order of several tens to several hundreds microns and ink-discharging port plane 55 in the direction perpendicular to the ink-discharging port plane 55, i.e., in the ink discharging direction (arrowed direction shown in FIG. 13). Therefore, the vibration can fatally crack these structures and recording element substrate 2 itself.
A recording element substrate is the most important and expensive of the components of an ink jet recording cartridge. The method which can cause defects, e.g., cracks, in the substrates in the final stage of the cartridge production process will make it difficult to supply the cartridges to the users at a reasonable price.
One approach against cracking to reduce the defects is to increase a vertical vibration frequency to 40 kHz in order to halve the amplitude at the horn tip. However, it is impossible to completely avoid the cracking by increasing the frequency, because the gravity acting on the ink discharging structure, including the hollows, changes little whether the frequency is 20 or 40 kHz.
Use of ultrasonic horizontal vibration, as disclosed by Japanese Patent Application Laid-Open No. H10-16244, is one approach. This method takes out horizontal vibration from the side of a horn designed to vertically oscillate for ultrasonic welding. In the horn 62 shown in FIG. 14, the vertical vibration from the booster 61 oscillates the side 63 of the horn 62 in the horizontal direction, to be transmitted to the work 64. The vibration decay from the horizontal vibration 65 to the horizontal vibration 66 as it moves from the side 63 to the center 62. This limits applicability of this method to a practical part size of 10 mm or so (length of the welded region). In other words, it is applicable to very small parts, e.g., recording element substrate, as described in the patent document. When applied to ink tank production, the method may not secure a sufficient strength of the welded interface, resulting from uneven welding.
The vibration welding method disclosed by Japanese Patent Application Laid-Open No. H09-94973 is developed for production of ink tanks of large size and complex shape. The method disclosed by Japanese Patent Application Laid-Open No. H10-16249 is not intended to bond an electronic part, e.g., recording element substrate, to an integrated structure. The patent document is silent on problems including vibration transmission to the outer surface of an ink tank housing, although describing prevention of deformation of the ink tank itself.
Another method winds a vibration-absorbing material or the like around an ink tank box, which is made of a filler-containing material, to prevent transmission of the vibration from the upper side of the ink tank to which a lid is bonded to a recording element substrate on the bottom surface of the ink tank, via the box outside. This method, although capable of reducing the transmitted vibration, cannot sufficiently prevent cracking of the substrate, described above.
Therefore, various methods have been adopted to prevent vibration transmission. Some of these methods include reduction of glass fiber content; changing the material itself; bonding a recording element substrate after a lid is bonded; unitization of recording element substrates, which are bonded by calking under heating after they are incorporated; and fixing a substrate by an adhesive agent. A method which bonds a recording element substrate after a lid is bonded may have limited applicable adhesive agents. A method which unitizes recording element substrates may need substrates of larger size, which can push up the cost.